1. Field of the Invention
The present invention relates in general to a thin film capacitor, and more particularly, to a thin film capacitor using a perovskite type dielectric film with a specific distribution profile along the growth direction, which capacitor is capable of reducing electric current leakage and enhancing service life of devices.
2. Description of the Related Art
Thin film ABO3 perovskite type dielectric materials, such as barium strontium titanate (BST: (Ba,Sr)TiO3), are currently being investigated for applications in microwave and RF devices and as charge storage devices for decoupling capacitor and DRAM applications. For these applications a high capacitance density, low leakage current, reduced dielectric loss, and long service life are required.
One of the major problems impeding the use of polycrystalline high dielectric constant oxide thin films, such as (Ba,Sr)TiO3, in device applications is achieving capacitance densities sufficient for device applications while maintaining low leakage with good service life.
Japanese Patent Registration No. 2929435 (corresponding to U.S. Pat. No. 5,783,253) discloses a technique for forming a dielectric film with improved physical and electrical characteristics, achieving a higher dielectric constant and smooth surfaces. With this method, a first BST film of a Barium composition x (BaxSr1-x) is formed, and then a second BST film of a different Ba composition x′ (x′=0.5) (Ba0.5Sr0.5) is formed over the first BST film. The first BST film serves to improve the surface roughness, and the second BST film serves to achieve a higher dielectric constant.